Device for detecting an attack against an integrated circuit

ABSTRACT

An integrated circuit including an intrusion attack detection device. The device includes a single-piece formed of a conductive material and surrounded with an insulating material and includes at least one stretched or compressed elongated conductive track, connected to a mobile element, at least one conductive portion distant from said piece and a circuit for detecting an electric connection between the piece and the conductive portion. A variation in the length of said track in an attack by removal of the insulating material, causes a displacement of the mobile element until it contacts the conductive portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of prior U.S. patent application Ser. No.12/538,030, filed Aug. 7, 2009, entitled DEVICE FOR DETECTING AN ATTACKAN INTEGRATED CIRCUIT which application claims the priority benefit ofFrench patent application number 08/55552, filed on Aug. 13, 2008,entitled DEVICE FOR DETECTING AN ATTACK AN INTEGRATED CIRCUIT, whichapplications are hereby incorporated by reference to the maximum extentallowable by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a device for detecting attacks bycontact on an integrated circuit. This type of attacks is generallycalled an “intrusion attack” and comprises applying conductive probesdirectly on areas of the integrated circuit to sample signals therefrom.In an integrated circuit, the active areas contain circuits forprocessing data which may be confidential, such as for example in bankcard chips or access-control chips in toll television applications.

2. Discussion of the Related Art

To protect the circuits located in the active area from any fraudulentintrusion, it is known to use a shield covering the entire circuitsurface or part of it. This shield is generally formed of one or ofseveral conductive paths formed in one or several metallization levelsabove the active area to be protected.

The aim of such conductive paths is to detect a discontinuity or anyelectric modification of their properties, for example, their resistanceor capacitance. The conductive paths run along the entire surface oronly an area of the circuit to be protected, in an irregular and randommanner. If a “hacker” attempts to cross the metallization levelcontaining the path, by introduction of one or several probes, adetection circuit is supposed to detect a rupture in the conductivepath.

A disadvantage of such a solution is that it does not enable to detectthe removal of the insulating layers covering the conductive path. Oncethe conductive path has been exposed, a “hacker” might double thisconductive path with an external section to simulate an electriccontinuity. The conductive path could then be interrupted without thisbeing detected.

SUMMARY OF THE INVENTION

At least one embodiment of the present invention aims at improving thedetection of attacks by intrusion on an integrated circuit by enablingto detect the removal of insulating layers covering the integratedcircuit.

Thus, an embodiment of the present invention provides an integratedcircuit comprising an intrusion attack detection device. The devicecomprises a single-piece formed of a conductive material and surroundedwith an insulating material and comprising at least one stretched orcompressed elongated conductive track, connected to a mobile element, atleast one conductive portion distant from said piece and a circuit fordetecting an electric connection between the piece and the conductiveportion. This results in a variation in the length of said track in anattack by removal of the insulating material, causing a displacement ofthe mobile element until it contacts the conductive portion.

According to an embodiment of the present invention, the single-piececomprises a first bar extending along a first direction, a second barextending along a second direction inclined with respect to the firstdirection and connected to a first lateral surface of the first bar atthe level of a first junction area, and a third bar extending along athird direction inclined with respect to the first direction andconnected to a second lateral surface of the first bar, opposite to thefirst lateral surface, at the level of a second junction area, the firstand second junction areas being shifted along the first direction. Theat least one conductive portion is distant from the first, second, andthird bars and arranged opposite to the first or second lateral surface.This results in a variation in the length of the second and third barsin the attack by removal of the insulating material, causing a pivotingof the first bar until it contacts the conductive portion.

According to an embodiment of the present invention, the first barcomprises first and second ends. The conductive portion is arrangedopposite to the first lateral surface, at the level of the first end,the circuit comprising an additional conductive portion arrangedopposite to the second lateral surface, distantly from the first,second, and third bars, at the level of the second end. This results ina variation of the length of the second and third bars in the attack byremoval of the insulating material, causing a pivoting of the first barso that the first end comes into contact with the conductive portion andthat the second end comes into contact with the additional conductiveportion.

According to an embodiment of the present invention, the second barcontinues in a first track of the conductive material of largercross-section and the third bar continues in a second track of theconductive material of larger cross-section.

According to an embodiment of the present invention, the second andthird bars belong to a conductive path.

According to an embodiment of the present invention, the cross-sectionof the second bar decreases at the level of the first junction area andthe cross-section of the third bar decreases at the level of the secondjunction area.

According to an embodiment of the present invention, the first barcomprises a tapered surface for bearing against the conductive portionduring the pivoting of the first bar.

According to an embodiment of the present invention, the second andthird directions are parallel to each other and perpendicular to thefirst direction.

An embodiment of the present invention also provides a method formanufacturing an integrated circuit comprising a device for detecting anattack by contact, comprising the steps of forming a single-piece formedof a conductive material and surrounded with an insulating material andcomprising at least one elongated conductive track connected to a mobileelement, at least one conductive portion distant from said piece and acircuit for detecting the creation of an electric connection between thepiece and the conductive portion and of annealing. This results in thecreation of tensile or compressive stress in said conductive track andin a variation of the length of said track in an attack by removal ofthe insulating material, causing a displacement of the mobile elementuntil it contacts the conductive portion.

The foregoing objects, features, and advantages of the present inventionwill be discussed in detail in the following non-limiting description ofspecific embodiments in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is intended to show the state of the art;

FIG. 2 is a simplified top view of a device for detecting attacks bycontact with an integrated circuit according to an embodiment of thepresent invention;

FIG. 3 is a simplified cross-section view of the detection device ofFIG. 2;

FIG. 4 is a cross-section view similar to FIG. 3 illustrating theprinciple of an attack by contact;

FIG. 5 is a view similar to FIG. 2 illustrating the operation of thedetection device according to the present embodiment of the invention inan attack by contact;

FIG. 6 shows the variation of an operating parameter of the detectiondevice of FIG. 2 according to a characteristic dimension of thedetection device; and

FIGS. 7 and 8 are top views of details of detection devices according toother embodiments of the present invention.

DETAILED DESCRIPTION

For clarity, the same elements have been designated with the samereference characters in the different drawings and, further, as usual inthe representation of integrated circuits, the various drawings are notto scale. In the following description, an integrated circuit comprisinga substrate (for example, a solid semiconductor substrate, asilicon-on-insulator substrate (SOI), etc.) covered with a stack oflayers of an insulating material at the level of which metal tracks ofdifferent metallization levels are provided is considered. The metaltracks of a given metallization level may be arranged on the surface ofan insulating layer or formed in an insulating layer, leveling thesurface thereof. The metal tracks most remote from the substrate arecalled metal tracks of the last metallization level, or uppermetallization level. The metal tracks of the last metallization levelare covered with an insulating layer, generally called a passivationlayer.

According to an embodiment of the present invention, a device fordetecting the removal of an insulating layer covering metal tracks of agiven metallization level is formed, at least partly, by metal tracks ofthe given metallization level. Advantageously, according to anembodiment, the metal tracks forming the detection device may alsobelong to a conductive path of a protection shield. An embodiment of thepresent invention is based on the fact that a conventional method formanufacturing an integrated circuit causes the appearance of tensilestress in the metal tracks of the different metallization levels. Thisis due to the fact that an anneal is generally performed once the metaltracks and the insulating layers have been formed. The anneal causes agrowth of the grains of the metal tracks and a decrease in the grainboundary density. This creates tensile stress in the metal tracks, giventhat the insulating material which surrounds them forces them to keeptheir shape. The removal of the insulating material surrounding themetal tracks relieves the stress in these tracks. An embodiment of thepresent invention provides a device for detecting the removal of theinsulating material in an intrusion attack. The device comprises amechanical switch comprising a mobile element which is displaced onrelief of the stress to establish an electric contact. The creation ofthe electric contact is detected and is representative of the removal ofthe insulating material.

FIG. 1 is a perspective view of an integrated circuit conventionallyprovided with a protection shield. The circuit comprises a substrate Scovered with a stack of insulating layers to which are associateddifferent metallization levels M1 . . . Ms. A conductive path Ldelimited by terminals V and W is formed in one of these levels, forexample, upper metallization level Ms. Conductive path L is connected atits ends to a circuit, not shown, capable of detecting an interruptionof conductive path L.

FIG. 2 shows a detection device 5 according to an embodiment of thepresent invention. Device 5 comprises a mechanical switch 10 connectedto a detection circuit C. More specifically, FIG. 2 is a partialsimplified top view of metal tracks of a same metallization level of anintegrated circuit forming switch 10 according to an embodiment of thepresent invention, detection circuit C being schematically representedby a block. Switch 10 may be duplicated at several locations at thelevel of a same metallization level. It may further be duplicated inseveral metallization levels of the same integrated circuit.

Switch 10 is formed at the level of a conductive path L comprising firstand second metal tracks 12, 14. It comprises an arm 16 corresponding toa metal track of length L1, of width l1, and extending along arectilinear central axis Δ1. Arm 16 continues track 12 and has across-section smaller than the cross-section of track 12. Switch 10further comprises an arm 18 corresponding to a metal track of length L2,of width l2, and extending along a rectilinear central axis Δ2. Arm 18continues track 14 and has a cross-section smaller than thecross-section of track 14. Axes Δ1 and Δ2 are, for example, parallel. Inthe present embodiment, arms 16, 18 substantially have a constantcross-section.

Switch 10 further comprises a bar 20 corresponding to a metal trackhaving a length L3, a width l3, and extending along a rectilinearcentral axis Δ3 perpendicular to axes Δ1 and Δ2. Bar 20 comprises acentral portion 22 and two free ends 23, 24. Central portion 22comprises two opposite lateral surfaces 25, 26. Switch 10 is symmetricalwith respect to a plane of symmetry P which corresponds to the planeperpendicular to axis Δ3 equidistant from ends 23 and 24. Call O theintersection point between plane P and axis Δ3. Call P′ the planeperpendicular to axes Δ1 and Δ2 and containing axis Δ3. At the endopposite to track 12, arm 16 is connected to surface 25 of centralportion 22 at the level of a junction area 27 and, at the end oppositeto conductive track 14, arm 18 is connected to surface 26 of centralportion 22 at the level of a junction area 28. Arms 16, 18 are thusarranged on either side of bar 20. Further, arms 16, 18 are located oneither side of plane P. Call spacing ec the distance, measured alongdirection Δ3, between the middle of junction area 27 and the middle ofjunction area 28, that is, in the present embodiment, between axes Δ1and Δ2.

Switch 10 further comprises metal tracks 29, 30. Track 29 is arranged onthe same side of bar 20 as arm 16 and extends opposite to a portion ofsurface 25 of central portion 22 close to end 23. Track 30 is arrangedon the same side of bar 20 as arm 18 and extends in front of a portionof surface 26 of central portion 22 on the side of end 24. Tracks 29 and30 are connected to circuit C, which is capable of detecting whethertracks 29, 30 are electrically connected to each other.

In the embodiment shown in FIG. 2, arms 16, 18, tracks 12, 14, and bar20 are made of a single piece.

FIG. 3 shows a partial simplified cross-section view of switch 10 alongline A-A. Switch 10 is formed at the level of an integrated circuit 31comprising a semiconductor substrate 32, for example, made of silicon,covered with a stack of insulating layers at the level of which arearranged metal tracks of different metallization levels. As an example,metal tracks 34, 36 of metallization level Ms−1 leveling the surface ofan insulating layer 38 have been shown. An insulating layer 40 coveringinsulating layer 38 and metal tracks 36 and 34 has further been shown.The metal tracks of metallization level Ms 20, 29 extend on insulatinglayer 40. As an example, metal tracks 34, 36 are made of copper andmetal tracks 20, 29 are made of aluminum. An insulating layer 46, calledpassivation layer, covers metal tracks 20, 29 and insulating layer 40.Layers 40, 46 are made of a same insulating material, for example,silicon oxide.

The method for manufacturing integrated circuit 31 comprises an annealstep which comprises the step of, after the forming of insulating layer46 covering metal tracks 20, 29, heating integrated circuit 31 up to atemperature, for example, on the order of a few hundreds of degrees, forexample, 400° C., for several tens of minutes, for example, 50 minutes.The anneal step causes an increase in the size of the metal grains ofthe metal tracks, in particular the metal grains in arms 16, 18 bydecrease of the density of the grain boundaries. This increase in thegrain size creates tensile stress in the metal grains of arms 16, 18.This tensile stress cannot be relieved because of the presence ofinsulating layers 40, 46 which surround arms 16, 18 and force them tokeep their initial shapes.

FIG. 4 is a view similar to FIG. 3 and illustrates the principle of anattack by contact. Such an attack comprises an initial step of etchingan opening 50 at the surface of integrated circuit 31 where the contactsare desired to be taken. Opening 50 is formed by etching of insulatinglayer 46. Since insulating layers 40 and 46 are formed of the sameinsulating material, it is not possible to accurately control the depthof opening 50. If the attack is performed in the region of circuit 31containing switch 10, for example, to duplicate conductive path L,opening 50 will at least partially penetrate into insulating layer 40.After the forming of opening 50, bar 20 is completely disengaged andarms 16 and 18 are at least partially disengaged.

The removal of the insulating material surrounding arms 16, 18 resultsin a relieving of the tensile stress in arms 16, 18, that is, a decreaseof lengths L1 and L2. Since arms 16, 18 remain anchored at one end totracks 12, 14, their shortening causes a pivoting of bar 20 aroundcenter O, with axis Δ3 substantially remaining in a plane perpendicularto plane P. Bar 20 pivots enough to come into contact with metal tracks29, 30.

FIG. 5 is a detail view of FIG. 2 which shows the state of switch 10after the etching of opening 50. Since arms 16 and 18 are not inprolongation of each other, their shortening has caused a pivoting ofbar 20. A slight deformation of arms 16, 18 by buckling can be observed.Call clearance D of bar 20 the distance between the edge of end 24closest to plane P′ and plane P′ after the stress has been relieved.

Detection circuit C connected to tracks 29, 30 detects the coming intocontact of bar 20 with metal tracks 29, 30. This may be interpreted ascorresponding to a contact attack and may cause the stopping of theoperation of integrated circuit 31.

FIG. 6 shows an example of a curve 51 of the variation, according tospacing ec, of clearance D observed in the absence of tracks 29, 30.Curve 51 is obtained for a switch 10 for which lengths L1, L2, and L3are equal to 100 μm, for which widths l1, l2, l3 are equal to 2 μm, andfor which the thickness of the metal tracks of metallization level Msis, for example, on the order of 0.3 μm. It is desirable for clearance Dof bar 20 to be as large as possible to ensure for a contact to alwaysbe present between bar 20 and metal tracks 29, 30 in case of an attack.In the previously-mentioned example, a clearance D on the order of 4.5μm is obtained for a spacing ec on the order of 4 μm.

In the present embodiment, switch 10 is formed at the level of aconductive path L belonging to a protection shield. Arms 16, 18 and bar20 electrically connect tracks 12, 14 together. Tracks 12 and 14 areconnected to a circuit capable of detecting an interruption ofconductive path L. This provides an additional protection, in additionto the protection provided by switch 10. According to an alternativeembodiment, only metal track 29 is present. In this case, a circuit iscapable of detecting whether an electric contact has been createdbetween metal track 29 and one of tracks 12 or 14. According to anothervariation, tracks 29 and 30 may correspond to metal pads. This may beadvantageous when several switches 10 are arranged adjacent to oneanother.

FIG. 7 shows a detail view of a switch 52 according to anotherembodiment of the present invention. Switch 52 has the same structure asswitch 10, except that arm 16 comprises, at the level of the endconnected to bar 20, a portion 54 with a decreasing cross-section, sothat junction area 27 has a reduced cross-section, of width l4, withrespect to arm 16. Similarly, arm 18 comprises, at the level of the endconnected to bar 20, a portion 56 with a decreasing cross-section, sothat junction area 28 has a reduced cross-section, of width l5, withrespect to arm 18. Junction areas 27, 28 of switch 52 deform more easilyduring the pivoting of bar 20 than junction areas 27, 28 of switch 10which have a greater cross-section. This enables, for the same spacing,to obtain a larger clearance D than when arms 16, 18 are of constantcross-section. As an example, for a switch 52 for which lengths L1, L2,and L3 are equal to 100 μm, for which widths l1, l2, l3 are equal to 2μm, for which the thickness of the metal tracks of metallization levelMs is on the order of 0.3 μm, and for which widths l4 and l5 are on theorder of 0.2 μm, a clearance D on the order of 10 μm is obtained, in theabsence of tracks 29, 30, for a spacing ec on the order of 4 μm.

Generally, the shape of junction areas 27, 28 is determined to enable toobtain the largest possible clearance D of bar 20 in the absence oftracks 29, 30 while ensuring a sufficient mechanical resistance ofswitch 10. According to an example, each junction area 27, 28 may have,in a plane perpendicular to plane P, the shape of a funnel. According toanother example, each junction area 27, 28 may comprise throughopenings.

FIG. 8 shows a switch 60 according to another embodiment of the presentinvention. Switch 60 comprises, at each end 23 of bar 20, a taperedsurface 62 which is oriented so that, in the pivoting of bar 20, taperedsurface 62 ends up bearing against metal track 29. This enables toimprove the contact between bar 20 and metal track 29.

In the previously-described embodiments, switch 10, 52, 60 is formed byportions of a conductive material in which tensile stress is createdduring the anneal step of the integrated circuit manufacturing method.As a variation, the switch may be formed of portions of a conductivematerial in which compressive stress appears in the anneal step. Thematerial is, for example, a semiconductor material such as polysilicon.Thereby, when the stress is relieved, arms 16, 18 of the switch tend tolengthen. In this case, as compared with switch 10 shows in FIG. 2, arms16 is arranged to the right of plane P and arm 18 is arranged to theleft of plane P so that bar 20 pivots in the right direction when thestress is relieved to ensure the electric connection between metaltracks 29, 30.

Specific embodiments of the present invention have been described.Various alterations and modifications will occur to those skilled in theart. In particular, in the previously-described embodiments, switch 10has a symmetrical shape. However, this is not compulsory. Further, inthe previously-described embodiments, arms 16, 18 and bar 20 have,before pivoting, rectilinear shapes. However, arms 16, 18 and bar 20 mayhave, before pivoting, curved shapes.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

What is claimed is:
 1. A method for manufacturing an integrated circuitcomprising a device for detecting an attack by contact, comprising thesteps of: forming a single-piece formed of a conductive material andsurrounded with an insulating material and comprising at least oneelongated conductive track connected to a mobile element, at least oneconductive portion distant from said piece and a circuit for detectingthe creation of an electric connection between the piece and theconductive portion; and annealing, which results in the creation oftensile or compressive stress in said conductive track and in avariation of the length of said track in an attack by removal of theinsulating material, causing a displacement of the mobile element allthe way until it contacts the conductive portion.
 2. A method formanufacturing an integrated circuit as defined in claim 1, whereinforming a single-piece comprises: forming a first bar extending along afirst direction; forming a second bar extending along a second directioninclined with respect to the first direction and connected to a firstlateral surface of the first bar at a first junction area; and forming athird bar extending along a third direction inclined with respect to thefirst direction and connected to a second lateral surface of the firstbar, opposite to the first lateral surface, at a second junction area,the first and second junction areas being shifted along the firstdirection, wherein the at least one conductive portion is spaced fromthe first, second and third bars and arranged opposite to the first orsecond lateral surface, which results in a variation in the length ofthe second and third bars upon removal of the insulating material,causing movement of the first bar into contact with the at least oneconductive portion.
 3. A method for manufacturing an integrated circuitas defined in claim 2, wherein the first bar comprises first and secondends and wherein the at least one conductive portion is arrangedopposite to the first lateral surface, at the first end, furthercomprising forming an additional conductive portion arranged opposite tothe second lateral surface and spaced from the first, second and thirdbars, at the second end, wherein removal of the insulating materialcauses the first end to contact the at least one conductive portion andthe second end to contact the additional conductive portion.
 4. A methodfor manufacturing an integrated circuit as defined in claim 2, whereinthe second bar and the third bar each include a first portion of a firstwidth and a second portion of a second width larger than the firstwidth.
 5. A method for manufacturing an integrated circuit as defined inclaim 2, comprising forming the second and third bars as a conductivepath of the integrated circuit.
 6. A method for manufacturing anintegrated circuit as defined in claim 2, comprising forming the secondbar with a decreased cross-section at the first junction area andforming the third bar with a decreased cross-section at the secondjunction area.
 7. A method for manufacturing an integrated circuit asdefined in claim 2, comprising forming the first bar with a taperedsurface for bearing against the at least one conductive portion uponpivoting of the first bar.
 8. A method for manufacturing an integratedcircuit as defined in claim 2, wherein the second and third directionsare parallel to each other and perpendicular to the first direction. 9.A method for manufacturing an integrated circuit, comprising: forming afirst conductive element on a substrate; forming an insulating materialsurrounding at least part of the first conductive element; forming asecond conductive element on the substrate; spacing the secondconductive element from the first conductive element such that removalof the insulating material causes the first conductive element tocontact the second conductive element; and annealing the integratedcircuit such that at least the first conductive element is stretched orcompressed.
 10. A method for manufacturing an integrated circuit asdefined in claim 9, wherein forming the first conductive elementcomprises: forming a first conductive track extending along a firstdirection; forming a second conductive track extending along a seconddirection different from the first direction and connected to a firstlateral surface of the first conductive track at a first junction area;and forming a third conductive track extending along a third directiondifferent from the first direction and connected to a second lateralsurface of the first conductive track, opposite to the first lateralsurface, at a second junction area, the first and second junction areasbeing spaced along the first direction, wherein removal of theinsulating material causes movement of the first conductive track intocontact with the second conductive element.
 11. A method formanufacturing an integrated circuit as defined in claim 10, wherein thefirst conductive track includes a first end spaced from the secondconductive element, further comprising forming a third conductiveelement spaced from a second end of the first conductive track, whereinremoval of the insulating material causes pivoting of the firstconductive track so that the first end contacts the second conductiveelement and the second end contacts the third conductive element.
 12. Amethod for manufacturing an integrated circuit as defined in claim 10,wherein the second conductive track and the third conductive track eachinclude a first portion of a first width and a second portion of asecond width larger than the first width.
 13. A method for manufacturingan integrated circuit as defined in claim 10, comprising forming thesecond and third conductive tracks as a conductive path of theintegrated circuit.
 14. A method for manufacturing an integrated circuitas defined in claim 10, comprising forming the second conductive trackwith a width that decreases in a region of the first junction area andforming the third conductive track with a width that decreases in aregion of the second junction area.
 15. A method for manufacturing anintegrated circuit as defined in claim 10, comprising forming the firstconductive track with a tapered surface configured to contact the secondconductive element.
 16. A method for manufacturing an integrated circuitas defined in claim 10, wherein the second and third directions areparallel to each other and are perpendicular to the first direction. 17.A method for manufacturing an integrated circuit as defined in claim 10,further comprising forming a detection circuit coupled between thesecond and third conductive elements and configured to detect anelectrical connection therebetween.
 18. A method for manufacturing anintegrated circuit as defined in claim 9, wherein annealing theintegrated circuit comprises heating the integrated circuit to cause atensile stress in the second and third conductive tracks.
 19. A methodfor manufacturing an integrated circuit as defined in claim 9, whereinannealing the integrated circuit comprises heating the integratedcircuit to a temperature on the order of a few hundred degrees forseveral tens of minutes.
 20. A method for manufacturing an integratedcircuit as defined in claim 9, wherein annealing the integrated circuitcomprises heating the integrated circuit to 400° C. for 50 minutes.